Structured warnings and assertions

[ConnorBaker]

Important

This should be verified and reference specific code.

meta.broken and meta.platforms (or meta.badPlatforms) produce errors rarely provide actionable information for use in troubleshooting. As an example, a package may be marked as broken if a dependency isn't correctly configured or is an unexpected version; recommending users allow all broken packages is typically an unacceptable action toward resolving that problem.

Nixpkgs should provide support for structured warnings and assertions which describe why a package is marked as unavailable.

See also:

• [RFC 0127] Nixpkgs "problem" infrastructure NixOS/rfcs#127
• stdenv: support meta.broken as a string to explain why it's broken NixOS/nixpkgs#109407
• Stdenv overhaul broken flag NixOS/nixpkgs#140325
• check-meta.nix: Add package warnings NixOS/nixpkgs#177272
• nixos: reusable assertions NixOS/nixpkgs#207187
• lib.modules: init types checkAndMerge to allow adding 'valueMeta' NixOS/nixpkgs#391544